Add a script to trim OTA package for go/otaanalyzer

Test: th
Change-Id: Id3b5cdc0095c6b398e402e2165729cb9cb67b257
diff --git a/scripts/trim_ota_package.py b/scripts/trim_ota_package.py
new file mode 100644
index 0000000..df7f170
--- /dev/null
+++ b/scripts/trim_ota_package.py
@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+
+import zipfile
+import struct
+
+
+def readPayloadMetadata(zfp: zipfile.ZipFile, entry):
+  _MAGIC = b'CrAU'
+  # 8 bytes for version, 8 bytes for manifest length, 4 bytes for metadata signature length
+  HEADER_STRUCT = ">4sQQL"
+  HEADER_LEN = struct.calcsize(HEADER_STRUCT)
+  with zfp.open(entry) as fp:
+    header = fp.read(HEADER_LEN)
+    (magic, version, manifest_length,
+     metadata_signature_len) = struct.unpack(HEADER_STRUCT, header)
+    assert magic == _MAGIC
+    assert version == 2, "Unsupported major payload version " + str(version)
+    print(f"{manifest_length} {metadata_signature_len}")
+    return header + fp.read(manifest_length + metadata_signature_len)
+
+
+def main(argv):
+  if len(argv) != 3:
+    print("Usage:", argv[0], "<input file> <output file>")
+    return 1
+  infile = argv[1]
+  outfile = argv[2]
+  with zipfile.ZipFile(infile, "r") as inzfp, zipfile.ZipFile(outfile, "w") as outzfp:
+    for entry in inzfp.infolist():
+      if entry.filename.startswith("META") or entry.filename.endswith(".map"):
+        outzfp.writestr(entry, inzfp.read(entry))
+      elif entry.filename == "payload.bin":
+        outzfp.writestr(entry, readPayloadMetadata(inzfp, entry))
+
+
+if __name__ == '__main__':
+  import sys
+  sys.exit(main(sys.argv))